In the past decade, particle-mediated acceleration of material, particularly genetic material, into living cells and tissues has emerged as an important tool of plant and animal biotechnology. Transient expression and germ line integration of introduced DNA has been demonstrated in microorganisms, plants, and animals.
As the fundamentals of the technology have been worked out, attention has increasingly shifted toward development of devices that offer the operator the ability to perform a series of particle-mediated gene transfers sequentially in rapid succession. Such a device would be particularly advantageous for use in mass immunization of humans or domesticated animals with genetic vaccines.
One limitation of existing particle-mediated gene transfer devices is the form in which the sample is provided. In all such devices, the sample is deposited upon the surface of small, dense particles of a material such as gold or platinum. The coated-particles are themselves then coated onto either a rigid surface, such as a metal plate, or onto a carrier sheet made of a fragile material such as mylar. The coated sheet is then accelerated toward a target. This approach has several advantages as well as some disadvantages. The advantages have to do with the fact that the planar sheet generates a very uniform spread of accelerated particles. One disadvantage is that, each particle-coated plate or carrier sheet is prepared individually and may be used only once, making particle acceleration a time-consuming and inefficient process, particularly when many repetitive gene transfers are envisioned. Each coated carrier sheet is relatively large and must be handled with care, to avoid damage or contamination. It is also sometimes difficult to distinguish the useful coated side of a carrier sheet from the uncoated side. Improper positioning of the carrier sheet can reduce throughput and can result in wasted samples.
The distribution or spread of the pattern of carrier particles may be more critical for some applications, i.e. when germ line events are desired, than for other applications, especially when only transient expression of the introduced genes is needed. When an infrequent germline transformation event is desired, it is necessary to uniformly accelerate particles toward a large area of cells or tissues. To date therefore, it has been considered desirable to distribute the coated-particles as a monolayer on a relatively large surface before accelerating them toward a target to maximize the number of cells receiving particles under precisely uniform conditions, and to thereby increase the likelihood that one cell will undergo a germline transformation. In contrast, when accelerating particles into cells to induce transient gene expression in somatic tissues such as skin, there is a less compelling need to make precisely uniform the acceleration of the particles, since adequate expression can take place even with low numbers of cells actually penetrated by particles. Therefore, particle delivery techniques that to date have been undesirable now become desirable.
To overcome these and other limitations, what is desired is a high throughput gene delivery apparatus that can accept a plurality of samples for rapid and sequential delivery into target tissues. What is also desired is a sample storage and delivery platform that is more durable, and easier to prepare, store, and handle than existing platforms.